Rapid microwave-assisted liquid phase conversion of bio-ethanol to n-butanol over a heterogeneous catalyst

Abstract

A sustainable bio-based fuel industry is dependent on finding efficient technologies for the production of biofuels. A microwave-assisted method to produce bio-butanol from bio-ethanol in liquid phase was investigated using a 2-level factorial design with catalyst type and loading, reaction temperature and reaction time as variables. A combined severity factor (CSF) was used to quantify the combined effect of all reaction conditions on ethanol conversion and butanol selectivity. From the results, it could be qualitatively deduced that the reaction initially followed the Guerbet mechanism for formation of butanol, but gradually shifted toward the direct coupling mechanism as reaction conditions became more severe with 50% of the butanol produced at a CSF of 6, produced through the direct coupling mechanism. The overall reaction order and observed specific reaction rate was determined as 1.54 ± 0.26 and 2.91·10−6 ± 2.36·10−7 g.0.54.L−0.54.s−1 respectively. Both high ethanol conversions (76.6 wt%) and high butanol selectivity (60 wt%) could be obtained in a very short reaction time (60 minutes). The results represent an improvement in reaction time, ethanol conversion and butanol selectivity of 300%, 47% and 16.7% respectively compared to previously reported data. This represents a significant step towards realizing an affordable low-carbon drop-in fuel for a low carbon economy.